/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.context;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.beans.BeanUtils;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextException;
import org.springframework.context.ApplicationContextInitializer;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.core.GenericTypeResolver;
import org.springframework.core.annotation.AnnotationAwareOrderComparator;
import org.springframework.core.env.ConfigurableEnvironment;
import org.springframework.core.io.ClassPathResource;
import org.springframework.core.io.support.PropertiesLoaderUtils;
import org.springframework.lang.Nullable;
import org.springframework.util.ClassUtils;
import org.springframework.util.ObjectUtils;
import org.springframework.util.StringUtils;

import javax.servlet.ServletContext;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.Properties;
import java.util.concurrent.ConcurrentHashMap;

/**
 * Performs the actual initialization work for the root application context.
 * Called by {@link ContextLoaderListener}.
 *
 * <p>Looks for a {@link #CONTEXT_CLASS_PARAM "contextClass"} parameter at the
 * {@code web.xml} context-param level to specify the context class type, falling
 * back to {@link org.springframework.web.context.support.XmlWebApplicationContext}
 * if not found. With the default ContextLoader implementation, any context class
 * specified needs to implement the {@link ConfigurableWebApplicationContext} interface.
 *
 * <p>Processes a {@link #CONFIG_LOCATION_PARAM "contextConfigLocation"} context-param
 * and passes its value to the context instance, parsing it into potentially multiple
 * file paths which can be separated by any number of commas and spaces, e.g.
 * "WEB-INF/applicationContext1.xml, WEB-INF/applicationContext2.xml".
 * Ant-style path patterns are supported as well, e.g.
 * "WEB-INF/*Context.xml,WEB-INF/spring*.xml" or "WEB-INF/&#42;&#42;/*Context.xml".
 * If not explicitly specified, the context implementation is supposed to use a
 * default location (with XmlWebApplicationContext: "/WEB-INF/applicationContext.xml").
 *
 * <p>Note: In case of multiple config locations, later bean definitions will
 * override ones defined in previously loaded files, at least when using one of
 * Spring's default ApplicationContext implementations. This can be leveraged
 * to deliberately override certain bean definitions via an extra XML file.
 *
 * <p>Above and beyond loading the root application context, this class can optionally
 * load or obtain and hook up a shared parent context to the root application context.
 * See the {@link #loadParentContext(ServletContext)} method for more information.
 *
 * <p>As of Spring 3.1, {@code ContextLoader} supports injecting the root web
 * application context via the {@link #ContextLoader(WebApplicationContext)}
 * constructor, allowing for programmatic configuration in Servlet 3.0+ environments.
 * See {@link org.springframework.web.WebApplicationInitializer} for usage examples.
 *
 * @author Juergen Hoeller
 * @author Colin Sampaleanu
 * @author Sam Brannen
 * @since 17.02.2003
 * @see ContextLoaderListener
 * @see ConfigurableWebApplicationContext
 * @see org.springframework.web.context.support.XmlWebApplicationContext
 */
public class ContextLoader {

    /**
     * Config param for the root WebApplicationContext id,
     * to be used as serialization id for the underlying BeanFactory: {@value}.
     */
    public static final String CONTEXT_ID_PARAM = "contextId";

    /**
     * Name of servlet context parameter (i.e., {@value}) that can specify the
     * config location for the root context, falling back to the implementation's
     * default otherwise.
     * @see org.springframework.web.context.support.XmlWebApplicationContext#DEFAULT_CONFIG_LOCATION
     */
    public static final String CONFIG_LOCATION_PARAM = "contextConfigLocation";

    /**
     * Config param for the root WebApplicationContext implementation class to use: {@value}.
     * @see #determineContextClass(ServletContext)
     */
    public static final String CONTEXT_CLASS_PARAM = "contextClass";

    /**
     * Config param for {@link ApplicationContextInitializer} classes to use
     * for initializing the root web application context: {@value}.
     * @see #customizeContext(ServletContext, ConfigurableWebApplicationContext)
     */
    public static final String CONTEXT_INITIALIZER_CLASSES_PARAM = "contextInitializerClasses";

    /**
     * Config param for global {@link ApplicationContextInitializer} classes to use
     * for initializing all web application contexts in the current application: {@value}.
     * @see #customizeContext(ServletContext, ConfigurableWebApplicationContext)
     */
    public static final String GLOBAL_INITIALIZER_CLASSES_PARAM = "globalInitializerClasses";

    /**
     * Any number of these characters are considered delimiters between
     * multiple values in a single init-param String value.
     */
    private static final String INIT_PARAM_DELIMITERS = ",; \t\n";

    /**
     * Name of the class path resource (relative to the ContextLoader class)
     * that defines ContextLoader's default strategy names.
     */
    private static final String DEFAULT_STRATEGIES_PATH = "ContextLoader.properties";


    private static final Properties defaultStrategies;

    static {
        // Load default strategy implementations from properties file.
        // This is currently strictly internal and not meant to be customized
        // by application developers.
        try {
            ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, ContextLoader.class);
            defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
        } catch (IOException ex) {
            throw new IllegalStateException("Could not load 'ContextLoader.properties': " + ex.getMessage());
        }
    }


    /**
     * Map from (thread context) ClassLoader to corresponding 'current' WebApplicationContext.
     */
    private static final Map<ClassLoader, WebApplicationContext> currentContextPerThread =
            new ConcurrentHashMap<>(1);

    /**
     * The 'current' WebApplicationContext, if the ContextLoader class is
     * deployed in the web app ClassLoader itself.
     */
    @Nullable
    private static volatile WebApplicationContext currentContext;


    /**
     * The root WebApplicationContext instance that this loader manages.
     */
    @Nullable
    private WebApplicationContext context;

    /** Actual ApplicationContextInitializer instances to apply to the context. */
    private final List<ApplicationContextInitializer<ConfigurableApplicationContext>> contextInitializers =
            new ArrayList<>();


    /**
     * Create a new {@code ContextLoader} that will create a web application context
     * based on the "contextClass" and "contextConfigLocation" servlet context-params.
     * See class-level documentation for details on default values for each.
     * <p>This constructor is typically used when declaring the {@code
     * ContextLoaderListener} subclass as a {@code <listener>} within {@code web.xml}, as
     * a no-arg constructor is required.
     * <p>The created application context will be registered into the ServletContext under
     * the attribute name {@link WebApplicationContext#ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE}
     * and subclasses are free to call the {@link #closeWebApplicationContext} method on
     * container shutdown to close the application context.
     * @see #ContextLoader(WebApplicationContext)
     * @see #initWebApplicationContext(ServletContext)
     * @see #closeWebApplicationContext(ServletContext)
     */
    public ContextLoader() {
    }

    /**
     * Create a new {@code ContextLoader} with the given application context. This
     * constructor is useful in Servlet 3.0+ environments where instance-based
     * registration of listeners is possible through the {@link ServletContext#addListener}
     * API.
     * <p>The context may or may not yet be {@linkplain
     * ConfigurableApplicationContext#refresh() refreshed}. If it (a) is an implementation
     * of {@link ConfigurableWebApplicationContext} and (b) has <strong>not</strong>
     * already been refreshed (the recommended approach), then the following will occur:
     * <ul>
     * <li>If the given context has not already been assigned an {@linkplain
     * ConfigurableApplicationContext#setId id}, one will be assigned to it</li>
     * <li>{@code ServletContext} and {@code ServletConfig} objects will be delegated to
     * the application context</li>
     * <li>{@link #customizeContext} will be called</li>
     * <li>Any {@link ApplicationContextInitializer ApplicationContextInitializers} specified through the
     * "contextInitializerClasses" init-param will be applied.</li>
     * <li>{@link ConfigurableApplicationContext#refresh refresh()} will be called</li>
     * </ul>
     * If the context has already been refreshed or does not implement
     * {@code ConfigurableWebApplicationContext}, none of the above will occur under the
     * assumption that the user has performed these actions (or not) per his or her
     * specific needs.
     * <p>See {@link org.springframework.web.WebApplicationInitializer} for usage examples.
     * <p>In any case, the given application context will be registered into the
     * ServletContext under the attribute name {@link
     * WebApplicationContext#ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE} and subclasses are
     * free to call the {@link #closeWebApplicationContext} method on container shutdown
     * to close the application context.
     * @param context the application context to manage
     * @see #initWebApplicationContext(ServletContext)
     * @see #closeWebApplicationContext(ServletContext)
     */
    public ContextLoader(WebApplicationContext context) {
        this.context = context;
    }


    /**
     * Specify which {@link ApplicationContextInitializer} instances should be used
     * to initialize the application context used by this {@code ContextLoader}.
     * @since 4.2
     * @see #configureAndRefreshWebApplicationContext
     * @see #customizeContext
     */
    @SuppressWarnings("unchecked")
    public void setContextInitializers(@Nullable ApplicationContextInitializer<?>... initializers) {
        if (initializers != null) {
            for (ApplicationContextInitializer<?> initializer : initializers) {
                this.contextInitializers.add((ApplicationContextInitializer<ConfigurableApplicationContext>) initializer);
            }
        }
    }


    /**
     * Initialize Spring's web application context for the given servlet context,
     * using the application context provided at construction time, or creating a new one
     * according to the "{@link #CONTEXT_CLASS_PARAM contextClass}" and
     * "{@link #CONFIG_LOCATION_PARAM contextConfigLocation}" context-params.
     * @param servletContext current servlet context
     * @return the new WebApplicationContext
     * @see #ContextLoader(WebApplicationContext)
     * @see #CONTEXT_CLASS_PARAM
     * @see #CONFIG_LOCATION_PARAM
     */
    public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {
        // 防止注册多个 ContextLoader
        if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) {
            throw new IllegalStateException(
                    "Cannot initialize context because there is already a root application context present - " +
                    "check whether you have multiple ContextLoader* definitions in your web.xml!");
        }

        servletContext.log("Initializing Spring root WebApplicationContext");
        Log logger = LogFactory.getLog(ContextLoader.class);
        if (logger.isInfoEnabled()) {
            logger.info("Root WebApplicationContext: initialization started");
        }
        long startTime = System.currentTimeMillis();

        try {
            // 如果 context 就尝试创建一个
            // Store context in local instance variable, to guarantee that
            // it is available on ServletContext shutdown.
            if (this.context == null) {
                // 创建一个IOC容器
                this.context = createWebApplicationContext(servletContext);
            }
            if (this.context instanceof ConfigurableWebApplicationContext) {
                ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context;
                if (!cwac.isActive()) {
                    // The context has not yet been refreshed -> provide services such as
                    // setting the parent context, setting the application context id, etc
                    if (cwac.getParent() == null) {
                        // The context instance was injected without an explicit parent ->
                        // determine parent for root web application context, if any.
                        ApplicationContext parent = loadParentContext(servletContext);
                        // 设置父容器，默认是null
                        cwac.setParent(parent);
                    }
                    /**
                     * 1. 给IOC容器设置 spring.xml (如果存在)
                     * 2. 扩展 Environment 支持访问 web容器中的初始化参数
                     * 3. 拿到初始化参数（globalInitializerClasses、contextInitializerClasses） 反射构造出实例，回调返回对 IOC容器进行定制化
                     *      {@link ApplicationContextInitializer#initialize(ConfigurableApplicationContext)} 对IOC容器进行加工
                     * 4. 刷新IOC容器
                     * */
                    configureAndRefreshWebApplicationContext(cwac, servletContext);
                }
            }
            // 将IOC容器（这个是父容器）存到Application域中。
            servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);
            ClassLoader ccl = Thread.currentThread().getContextClassLoader();
            if (ccl == ContextLoader.class.getClassLoader()) {
                currentContext = this.context;
            } else if (ccl != null) {
                // 设置到 ThreadLocal 中
                currentContextPerThread.put(ccl, this.context);
            }

            if (logger.isInfoEnabled()) {
                long elapsedTime = System.currentTimeMillis() - startTime;
                logger.info("Root WebApplicationContext initialized in " + elapsedTime + " ms");
            }

            return this.context;
        } catch (RuntimeException | Error ex) {
            logger.error("Context initialization failed", ex);
            servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex);
            throw ex;
        }
    }

    /**
     * Instantiate the root WebApplicationContext for this loader, either the
     * default context class or a custom context class if specified.
     * <p>This implementation expects custom contexts to implement the
     * {@link ConfigurableWebApplicationContext} interface.
     * Can be overridden in subclasses.
     * <p>In addition, {@link #customizeContext} gets called prior to refreshing the
     * context, allowing subclasses to perform custom modifications to the context.
     * @param sc current servlet context
     * @return the root WebApplicationContext
     * @see ConfigurableWebApplicationContext
     */
    protected WebApplicationContext createWebApplicationContext(ServletContext sc) {
        /**
         * 拿到IOC容器的类对象：
         *      1. 从初始化参数拿
         *      2. 读取属性文件 `ContextLoader.properties` 这个是在 spring-web.jar 中写了一个
         * */
        Class<?> contextClass = determineContextClass(sc);
        if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
            throw new ApplicationContextException("Custom context class [" + contextClass.getName() +
                                                  "] is not of type ["
                                                  + ConfigurableWebApplicationContext.class.getName() + "]");
        }
        // 实例化出 IOC 容器
        return (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
    }

    /**
     * Return the WebApplicationContext implementation class to use, either the
     * default XmlWebApplicationContext or a custom context class if specified.
     * @param servletContext current servlet context
     * @return the WebApplicationContext implementation class to use
     * @see #CONTEXT_CLASS_PARAM
     * @see org.springframework.web.context.support.XmlWebApplicationContext
     */
    protected Class<?> determineContextClass(ServletContext servletContext) {
        // 尝试获取初始化属性：contextClass
        String contextClassName = servletContext.getInitParameter(CONTEXT_CLASS_PARAM);
        if (contextClassName != null) {
            try {
                return ClassUtils.forName(contextClassName, ClassUtils.getDefaultClassLoader());
            } catch (ClassNotFoundException ex) {
                throw new ApplicationContextException(
                        "Failed to load custom context class [" + contextClassName + "]", ex);
            }
        } else {
            // 获取属性
            contextClassName = defaultStrategies.getProperty(WebApplicationContext.class.getName());
            try {
                return ClassUtils.forName(contextClassName, ContextLoader.class.getClassLoader());
            } catch (ClassNotFoundException ex) {
                throw new ApplicationContextException(
                        "Failed to load default context class [" + contextClassName + "]", ex);
            }
        }
    }

    protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) {
        if (ObjectUtils.identityToString(wac).equals(wac.getId())) {
            // The application context id is still set to its original default value
            // -> assign a more useful id based on available information
            String idParam = sc.getInitParameter(CONTEXT_ID_PARAM);
            if (idParam != null) {
                wac.setId(idParam);
            } else {
                // Generate default id...
                wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
                          ObjectUtils.getDisplayString(sc.getContextPath()));
            }
        }

        // 双向奔赴，将 ServletContext 记录到 IOC容器中
        wac.setServletContext(sc);
        String configLocationParam = sc.getInitParameter(CONFIG_LOCATION_PARAM);
        if (configLocationParam != null) {
            // 设置Spring.xml
            wac.setConfigLocation(configLocationParam);
        }

        // The wac environment's #initPropertySources will be called in any case when the context
        // is refreshed; do it eagerly here to ensure servlet property sources are in place for
        // use in any post-processing or initialization that occurs below prior to #refresh
        ConfigurableEnvironment env = wac.getEnvironment();
        if (env instanceof ConfigurableWebEnvironment) {
            // 就是扩展IOC容器的Environment对象，可以访问到 web容器中的初始化参数
            ((ConfigurableWebEnvironment) env).initPropertySources(sc, null);
        }

        /**
         * 定制化Context，其实就是定制化IOC容器
         *
         * 根据在 ServletContext 配置的初始化类，用来加工IOC容器(父容器)
         *      1. 在实例化 ContextLoader 的时候，可以设置 {@link AbstractContextLoaderInitializer#registerContextLoaderListener(ServletContext)}
         *      2. 拿到配置在web容器中的属性信息：globalInitializerClasses、contextInitializerClasses 。反射实例化出 ApplicationContextInitializer
         *
         *      注：就是回调 {@link ApplicationContextInitializer#initialize(ConfigurableApplicationContext)} 对IOC容器进行加工
         * */
        customizeContext(sc, wac);
        // 刷新IOC容器
        wac.refresh();
    }

    /**
     * 根据在 ServletContext 配置的初始化类，用来加工IOC容器(父容器)
     * Customize the {@link ConfigurableWebApplicationContext} created by this
     * ContextLoader after config locations have been supplied to the context
     * but before the context is <em>refreshed</em>.
     * <p>The default implementation {@linkplain #determineContextInitializerClasses(ServletContext)
     * determines} what (if any) context initializer classes have been specified through
     * {@linkplain #CONTEXT_INITIALIZER_CLASSES_PARAM context init parameters} and
     * {@linkplain ApplicationContextInitializer#initialize invokes each} with the
     * given web application context.
     * <p>Any {@code ApplicationContextInitializers} implementing
     * {@link org.springframework.core.Ordered Ordered} or marked with @{@link
     * org.springframework.core.annotation.Order Order} will be sorted appropriately.
     * @param sc the current servlet context
     * @param wac the newly created application context
     * @see #CONTEXT_INITIALIZER_CLASSES_PARAM
     * @see ApplicationContextInitializer#initialize(ConfigurableApplicationContext)
     */
    protected void customizeContext(ServletContext sc, ConfigurableWebApplicationContext wac) {
        /**
         * 拿到配置在web容器中的属性信息：globalInitializerClasses、contextInitializerClasses，
         * 然后反射实例化成 Class 实例
         * */
        List<Class<ApplicationContextInitializer<ConfigurableApplicationContext>>> initializerClasses =
                determineContextInitializerClasses(sc);

        // 遍历 initializerClasses
        for (Class<ApplicationContextInitializer<ConfigurableApplicationContext>> initializerClass : initializerClasses) {
            // 拿到 ApplicationContextInitializer 上的泛型参数
            Class<?> initializerContextClass =
                    GenericTypeResolver.resolveTypeArgument(initializerClass, ApplicationContextInitializer.class);
            // 校验泛型类型
            if (initializerContextClass != null && !initializerContextClass.isInstance(wac)) {
                throw new ApplicationContextException(String.format(
                        "Could not apply context initializer [%s] since its generic parameter [%s] " +
                        "is not assignable from the type of application context used by this " +
                        "context loader: [%s]", initializerClass.getName(), initializerContextClass.getName(),
                        wac.getClass().getName()));
            }
            // 记录到属性中
            this.contextInitializers.add(BeanUtils.instantiateClass(initializerClass));
        }

        // 排序
        AnnotationAwareOrderComparator.sort(this.contextInitializers);
        for (ApplicationContextInitializer<ConfigurableApplicationContext> initializer : this.contextInitializers) {
            // 回调初始化化方法 加工 IOC 容器
            initializer.initialize(wac);
        }
    }

    /**
     * Return the {@link ApplicationContextInitializer} implementation classes to use
     * if any have been specified by {@link #CONTEXT_INITIALIZER_CLASSES_PARAM}.
     * @param servletContext current servlet context
     * @see #CONTEXT_INITIALIZER_CLASSES_PARAM
     */
    protected List<Class<ApplicationContextInitializer<ConfigurableApplicationContext>>>
    determineContextInitializerClasses(ServletContext servletContext) {

        List<Class<ApplicationContextInitializer<ConfigurableApplicationContext>>> classes =
                new ArrayList<>();

        String globalClassNames = servletContext.getInitParameter(GLOBAL_INITIALIZER_CLASSES_PARAM);
        if (globalClassNames != null) {
            for (String className : StringUtils.tokenizeToStringArray(globalClassNames, INIT_PARAM_DELIMITERS)) {
                classes.add(loadInitializerClass(className));
            }
        }

        String localClassNames = servletContext.getInitParameter(CONTEXT_INITIALIZER_CLASSES_PARAM);
        if (localClassNames != null) {
            for (String className : StringUtils.tokenizeToStringArray(localClassNames, INIT_PARAM_DELIMITERS)) {
                classes.add(loadInitializerClass(className));
            }
        }

        return classes;
    }

    @SuppressWarnings("unchecked")
    private Class<ApplicationContextInitializer<ConfigurableApplicationContext>> loadInitializerClass(String className) {
        try {
            Class<?> clazz = ClassUtils.forName(className, ClassUtils.getDefaultClassLoader());
            if (!ApplicationContextInitializer.class.isAssignableFrom(clazz)) {
                throw new ApplicationContextException(
                        "Initializer class does not implement ApplicationContextInitializer interface: " + clazz);
            }
            return (Class<ApplicationContextInitializer<ConfigurableApplicationContext>>) clazz;
        } catch (ClassNotFoundException ex) {
            throw new ApplicationContextException("Failed to load context initializer class [" + className + "]", ex);
        }
    }

    /**
     * Template method with default implementation (which may be overridden by a
     * subclass), to load or obtain an ApplicationContext instance which will be
     * used as the parent context of the root WebApplicationContext. If the
     * return value from the method is null, no parent context is set.
     * <p>The main reason to load a parent context here is to allow multiple root
     * web application contexts to all be children of a shared EAR context, or
     * alternately to also share the same parent context that is visible to
     * EJBs. For pure web applications, there is usually no need to worry about
     * having a parent context to the root web application context.
     * <p>The default implementation simply returns {@code null}, as of 5.0.
     * @param servletContext current servlet context
     * @return the parent application context, or {@code null} if none
     */
    @Nullable
    protected ApplicationContext loadParentContext(ServletContext servletContext) {
        return null;
    }

    /**
     * Close Spring's web application context for the given servlet context.
     * <p>If overriding {@link #loadParentContext(ServletContext)}, you may have
     * to override this method as well.
     * @param servletContext the ServletContext that the WebApplicationContext runs in
     */
    public void closeWebApplicationContext(ServletContext servletContext) {
        servletContext.log("Closing Spring root WebApplicationContext");
        try {
            if (this.context instanceof ConfigurableWebApplicationContext) {
                // 关闭IOC容器
                ((ConfigurableWebApplicationContext) this.context).close();
            }
        } finally {
            ClassLoader ccl = Thread.currentThread().getContextClassLoader();
            if (ccl == ContextLoader.class.getClassLoader()) {
                currentContext = null;
            } else if (ccl != null) {
                // 移除ThreadLocal中的值
                currentContextPerThread.remove(ccl);
            }
            // 从Application域中移除属性
            servletContext.removeAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);
        }
    }


    /**
     * Obtain the Spring root web application context for the current thread
     * (i.e. for the current thread's context ClassLoader, which needs to be
     * the web application's ClassLoader).
     * @return the current root web application context, or {@code null}
     * if none found
     * @see org.springframework.web.context.support.SpringBeanAutowiringSupport
     */
    @Nullable
    public static WebApplicationContext getCurrentWebApplicationContext() {
        ClassLoader ccl = Thread.currentThread().getContextClassLoader();
        if (ccl != null) {
            WebApplicationContext ccpt = currentContextPerThread.get(ccl);
            if (ccpt != null) {
                return ccpt;
            }
        }
        return currentContext;
    }

}
